<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .conyainer{
            background-color: green;
            overflow: hidden;
            /* BFC */
        }
        .box{
            margin: 100px;
            width: 100px;
            height: 100px;
            background-color: red;
            float: left;
            /* position:absolute;
            top: 0; */
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="box">

        </div>
        <div class="box">

        </div>
    </div>
</body>
</html>